Pursuant to 35 USC xc2xa7xc2xa7365(b) and 120, the priority of PCT/EP 00/00651 filed Jan. 28, 2000 and German Application No. DE 199 05 645.5 filed Feb. 11, 1999 is claimed.
Filter assemblies for vacuum filtration which are secured fluid-tight to filtrate receptacles are known. One such filter assembly is disclosed in EP 0 595 847 B1, comprising a supported flat filter sealed fluid-tight at its periphery so as to form a feed inlet chamber on the feed side of the filter. On the permeate side of the filter, a filtrate removal device protrudes into a filtrate-retaining chamber. A conduit penetrates the filtrate chamber of the filter assembly, with its distal end connected to a source of vacuum. The flat filter is a hydrophilic, microporous membrane having a plurality of hydrophobic portions. Upon the application of vacuum, the aqueous medium to be filtered flows over but not through the hydrophobic portions and permeates the hydrophilic portions of the membrane and is discharged through a downstream side filtrate discharge port to a filtrate receptacle. Entrained air bubbles, which are carried along with the filtration medium and would otherwise block the hydrophilic part of the membrane for filtration, are supposed to be diverted by the hydrophobic portions of the membrane.
A major drawback of such a filter assembly is that it permits a relatively small flow of filtrate to pass per unit time through the hydrophilic portions of the membrane. The reason for this small flow is that the hydrophilic membrane surface has a relatively small surface area due both to its flat construction and to the inclusion of hydrophobic portions thereon. This arrangement permits air bubbles to attach themselves to the hydrophilic portions of the membrane, causing them to be at least temporarily excluded as a filtering surface for as long as the air bubbles are not in turbulent flow on the hydrophobic portions of the membrane. Moreover, such a hybrid membrane becomes blinded very quickly, so that filter assemblies of this design are not suitable for vacuum filtration of larger quantities of liquid or for liquids carrying substances which deposit as films on membrane filters.
It is therefore a principal object of the invention to provide a vacuum filtration assembly whereby the above-noted disadvantages are overcome.
In accordance with the invention, a vacuum filter assembly is equipped with a cartridge-like filter element enclosed in a cylindrical housing so as to form an inlet chamber with the inlet chamber arranged radially about the filter element and in fluid communication with an upper chamber located axially above the filter element. The filter element comprises at least one tubular, pleated, hydrophilic and microporous membrane filter which is sealed fluid-tight by upper and lower end caps. A filtrate chamber is formed within the tubular membrane filter and is in fluid communication both with an outlet by an opening in the lower end cap, and with a filtrate receptacle which in turn is connected to a vacuum source. The upper end cap also has an opening sealed off by a hydrophobic gas-permeable membrane.
The invention may be employed for clear and sterile filtration of aqueous media, which are typically handled in working volumes of one liter in laboratories and in the technical aspects of biotechnology, chemical operations and medicinal research as well as in other scientific areas in which such filtration may be found necessary.